This invention relates to a transmission for propelling agricultural tractors in which a main transmission has, directly connected thereto, a speed increasing transmission part adapted to drive a right and left pair of dirigible front wheels at a greater average circumferential speed than a right and left pair of rear wheels.
An agricultural tractor of the type noted above has the front wheels adapted to be driven at increased speeds in order to make a small sharp turn at an end of the field. Conventionally, the speed increasing transmission part is directly connected to a bottom portion of the main transmission in order that the addition of the speed increasing transmission part may easily be effected without necessitating an extensive modification of the main transmission. This arrangement has a disadvantage that the attached speed increasing transmission part projects downwardly from the main transmission lowering the bottom of a transmission case relative to the ground. As a result, the transmission case tends to contact ridges and crops when the tractor carries out an operation while stradding the ridges.